THE RACING ALFA-ROMEO CYLINDER HEAD
The best of racing-cars is liable to trouble in the course of development. In the case of the Alfa-Romeo, a difficulty which has arisen since the days of the reliable 2.3-litre has been that of cylinder head cracking. This has been evident since several of the Ferarri 2.6 and 2.9litre monoposto cars have been imported to this country. R. O. Shuttleworth came up against the trouble and, we believe, practically admitted that he could not overcome it. Jack Bartlett, A. P. Ashby, and Jill Thomas have been others similarly affected. It would appear that the original design embraced fairly large valves and an 18 mm. sparking plug placed centrally, in light alloy heads, the diameter of which was 68 mm. in the case of the 2.6litre and 29-litre engines. In consequence, there was inadequate water jacketing around the valves and plugs and overheating took place, with the result that the heads cracked between the valve seats and plug aperture. As we announced last November, A. P. Ashby has redesigned the blocks of his 2.9-litre in an attempt to overcome these troubles. The manifold results are very interesting. It was decided that light alloy construction of the combined blocks and heads was unnecessary from both the weight-saving and cooling aspects, and Ashby’s new blocks (the Alfa has its eight cylinders arranged as two blocks of four) are cast in steel. It was, however, considered that this change of material would not, in itself, obviate the cracking and so Ashby altered the whole layout. 14 mm. sparking plugs are now used. These are still set in the centre line of the head, but they enter at an angle and have a slight bias towards the exhaust valves. Ashby has long held the view that motorcycle practice in respect of keeping the port areas small so as to promote adequate turbulence in hemispherical heads is correct. Consequently, his new heads have smaller ports, of a much improved formation, and beautifully polished. The valve seat width is reduced and the valve guides faired off, while the inlet valves are now larger than the exhaust valves. An interesting point is that the Alfa head had masked plugs to combat the
oil flung up from the sump, but by redesign of the base chamber baffles, Ashby is able to use exposed plugs, with, he hopes, further improvement in combustion and cooling. In order to completely lay the overheating bogy, a special flow of water is now directed round the exhaust valves, the water entering the heads via separate ribbed four branch manifolds set between the line of plugs and. the off-side camshaft cover. The valve actuation by twin centrally driven o.h. camshafts remains unchanged. Ashby has also improved the holding down studs, following trouble in this region, which we believe has also been experienced by the Bellevue stable. Apart from the improved blocks, a new inlet manifold system has been evolved to improve distribution. A combined manifold has separate passages to the ports, one blower feeding the centre four cylinders, the other the two outer
cylinders. The crankcase remains of alloy. New con-rods, under the Ashby patent, are fitted and ” four-cylinder ” exhaust manifolds are used.